Lattice Model of Equilibrium Polymerization.VI. Measures of Fluid Complexity and Search for Generalized Corresponding States

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Abstract:

Particle association in complex fluids containing charged, polar, or polymeric molecular species often leads to deviations from the corresponding states description of simple fluids in which the molecules are assumed to have relatively symmetric interactions and shapes. This fundamental problem is addressed by developing a minimal thermodynamic model of activated equilibrium polymerization solutions that incorporates effects associated with the competition between van der Waals and associative interactions, as well as features related to molecular anisotropy and many-body interactions. Because molecular selfassembly can strongly couple with fluid phase separation, evidence is also sought for associative interactions in the behavior of the second and third osmotic virial coefficients. In particular, the temperatures where the second and third virial coefficients, respectively,vanish, are found to contain valuable information about the relative strength of the associative and van der Waals interactions. The critical temperature Tc for phase separation, the critical composition jc, and the rectilinear diameter, describing the asymmetry of the coexistence curve for phase separation, along with the average cluster mass and extent of polymerization at the critical point, further specify the relevant interaction parameters of our model. Collectively, these characteristic properties provide a thermodynamic metric for defining fluid complexity and for use in developing a theoretically-based corresponding states relation for complex fluids.